NATO leaders are reportedly unhappy with what they perceive as an act of aggression near the borders of their member states.

“The deployment of missiles close to alliance borders that can carry nuclear warheads does not help to lower tensions,” a NATO representative told the German Press Agency. “We need more — not less — transparency and predictability on military activities to avoid incidents and the risk of misunderstandings.”

Russia said it’s not the first time they’ve used the nuclear missiles in training exercises. Russian defense ministry spokesman Igor Konashenkov shrugged off concerns, calling the move “not exceptional.”

Relations between the West and Russia have grown increasingly strained over the last year. NATO has voiced concerns over Russia’s annexation of Crimea. Russian President Vladimir Putin’s support of embattled Syrian President Bashar al-Assad has also angered Western allies.

NATO members Finland, Sweden, Estonia and Latvia have all reported airspace violations by Russia in recent months.

Russia isn’t the only nation moving troops around. At a summit in Warsaw earlier this year, NATO announced it was planning to deploy additional troops in Poland, as well as the Baltic states of Lithuania, Latvia and Estonia.